The present invention relates to a mask structure for cassettes of magnetic tape with means for locking with respect to the box-like shell.
As is known, cassettes of magnetic tape are constituted by a box-like shell produced by means of two mutually associable half-shells, which define in their interior the region of accommodation of the hubs on which the magnetic tape winds and unwinds.
In order to correctly locate the hubs inside the boxlike shell, masks are conventionally used which are constituted by sheet-like elements possibly shaped and covered with portions of material with low friction coefficient, which are interposed between the axial ends of the reel of magnetic tape and the inner wall of the box-like shell.
In order to position the masks with respect to the half-shells, so as to prevent said masks from moving during the step of coupling of the two half-shells, one or more holes were provided, generally located in the peripheral regions of the mask, with which studs engaged which, slightly forcing into said holes, created a force for the retention of the mask with respect to the half-shells, so as to prevent the displacement of the mask during the step of overturning of the half-shells for their mutual coupling.
This solution has been abandoned in the course of time, since it is scarcely practical from a functional point of view and poorly accepted from an aesthetical point of view, since said stud was clearly visible from outside.
In order to solve the problem using automatic packaging machines, the method was subsequently introduced of slightly wetting or dampening the surface of the mask in contact with the half-shell, so as to have an at least temporary adhesion, required to maintain the coupling between the mask and the half-shell during the assembly step.
Even this solution, however, is not free from disadvantages, since it is not infrequent that the unstable adhesion, determined by the wetting of the sheet-like element or by other methods or experiences currently in use, lead to an uncoupling of the sheet-like element from the half-shell; moreover, the wetting of the sheet-like element unavoidably creates residual humidity in the cassette.